Herpes simplex viruses are the causative agents in a number of mammalian infections, for example, such human diseases as keratitis, herpes labialis (cold sores), cutaneous herpes, herpes zoster, herpes genitalis, herpes encephalitis, neonatal herpes, herpetic whitlow and acute herpetic gingivostomatitis. Poxviruses, especially poxvirus variolae, are the causative agents of smallpox in man. No completely satisfactory antiviral agent combining high potency and low toxicity has yet been discovered. Accordingly, considerable research effort has been expended in attempts to discover a suitable agent.